The present invention relates to a brake system with hydraulic brake force boosting for use with motor vehicles. The system comprises a pedal-operated brake pressure generator connected to the wheel brakes by way of pressure fluid conduits, and further comprises an auxiliary pressure supply system and a control valve causing an auxiliary pressure proportional to the pedal force. The system further includes valve arrangements located in the pressure fluid conduits which valves, in one switching position, hydraulically connect the brake pressure generator to the wheel brakes and, after re-switching into a second switching position, connect the auxiliary pressure source in lieu of the brake pressure generator to the pressure fluid conduits leading to the wheel brakes. The system further comprises a pedal travel simulator permitting a travel of the pedal proportional to the pedal force.
Brake systems with a hydraulic brake force boosting of this type are known in the art, which comprise a master cylinder having a hydraulic brake force booster disposed upstream thereof, and which are equipped with an auxiliary pressure suppy system. The brake force booster consists of an auxiliary pressure control valve which, when the brake is applied, causes an auxiliary pressure proportional to the pedal force, which auxiliary pressure is transferred to the pistons in the master cylinder and/or directly, by way of a hydraulic connecting line, to the wheel brakes of a brake circuit. The static circuits of the master cylinder, in such arrangements, provide a pedal travel proportional to the pedal force.
Moreover, a hydraulic brake system has been suggested which, is a normal (i.e., non-defective operating condition) especially with an intact auxiliary pressure supply system, in any braking operation, immediately after actuating the brake pedal, switches over to dynamic pressure control (W. German published application No. P 3502018.0). By actuating the brake pedal, a controlled auxiliary pressure proportional to the pedal force is generated to re-switch pressure-controlled multidirectional valves thereby precluding drain of pressure fluid from the master cylinder and connecting instead the auxiliary pressure source to the wheel brakes. In that system, the master cylinder piston is enabled with the aid of a pedal travel simulator to cover despite the hydraulic blocking a distance in pedal-responsive manner. For that purpose, an additional piston is provided in the master cylinder which is displaceable against spring force. Pedal travel simulators of this type are relatively costly because they require a strong restoring spring permitting the required counter-force and an adequate pedal travel required for fine metering of the braking force.
It is, therefore, the object of the present invention to overcome the afore-described disadvantages by providing a pedal travel simulator suitable for hydraulic brake systems, permitting relatively low manufacturing efforts and compact construction.